Lead casing for pencil, and pencil thereof for writing, drawing, marking, plotting, and coloring

ABSTRACT

There is a lead casing for pencil for writing, drawing, marking, plotting, and/or coloring, made of a composition having, by weight relative to the total weight of the lead casing for pencil: a) from 50 to 95% of a mixture of polylactic acid and bio-polyethylene in a weight ratio polylactic acid/bio-polyethylene ranging from 60/40 to 90/10, and b) from 5 to 40% of vegetable fillers chosen in the group consisting of wood fibers.There is a pencil including the lead casing for the pencil of the disclosure for writing, drawing, marking, plotting, and/or coloring as well as a method for manufacturing such a pencil.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Application of InternationalApplication No. PCT/EP2019/085722, filed on Dec. 17, 2019, now publishedas WO2020/127320, which claims priority to EP18306714.9, filed on Dec.18, 2018, the entire contents of both of which are incorporated hereinby reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to a polymer-based lead casing forpencil. The is disclosure also relates to a method for manufacturing apencil comprising a lead casing according to the disclosure. Finally,the disclosure relates to the use of a pencil comprising a lead casingfor pencil according to the disclosure for writing, drawing, marking,plotting, and/or coloring.

DESCRIPTION OF THE RELATED ART

Two main families of thermoplastic polymers are used today in syntheticlead casings for pencils: styrenics such as polystyrene (PS) andacrylonitrile butadiene styrene (ABS) and polyolefins such aspolyethylene (PE) and polypropylene (PP). These polymers are all fromthe petroleum industry. For ecological reasons, it would be interestingto be able to replace such thermoplastic polymers with biorenewablepolymers.

The patent application FR2988643 describes a pencil whose lead casing(called the envelope portion in the application) is based on expandedsynthetic material. It teaches that the thermoplastic materials of thelead casing portion and the lead portion may be selected from styrenicpolymers such as polystyrene, polyolefins and biopolymers. Polylacticacid (PLA) is thus the only biopolymer cited, although the only exampleof lead casing is based on a polymer matrix of the styrenic family.

SUMMARY OF THE DISCLOSURE

The inventors have now observed that the use of PLA as the solethermoplastic polymer in the lead casing for pencil did not make goodmechanical properties in terms of resilience and impact resistance,which can cause problems in the manufacturing process and the sharpnessof the final pencil. Thus, PLA “alone” does not make a good substitutefor polymers derived from petroleum such as polystyrene in themanufacture of the lead casing for pencil.

The inventors, however, surprisingly observed that it was possible tomanufacture a lead casing for pencil having better mechanical propertiesto polystyrene-based lead casings by using as a thermoplastic polymer amixture of PLA with bio-polyethylene (bio-PE), another biopolymer, inspecific proportions, in combination with an appropriate content ofvegetable fillers chosen in the group consisting of wood fibers.

The present disclosure therefore relates to a lead casing for pencilwhich is made of a composition comprising (more specifically consistingessentially of, in particular consisting of), by weight relative to thetotal weight of the lead casing for pencil:

a) from 50 to 95%, more specifically from 60 to 90%, and even morespecifically from 70 to 90%, of a mixture of PLA and bio-PE in a weightratio PLA/bio-PE ranging from 60/40 to 90/10, andb) from 5 to 40%, more specifically from 7 to 30%, of vegetable fillerschosen in the group consisting of wood fibers.

Such polymer-based lead casings for pencil are intended to replacetraditional lead casings made of wood, and may be referred to “syntheticwood” or “body/core synthetic”. They allow the gripping of pencil andprotect the lead against breakage. They must be resistant to deformationfor not being bended or twisted, which would break the lead from inside.They must also be able to be cut by a traditional sharpener. They aregenerally made of polymer-based synthetic material whose density andsharpness are similar to those of wood and can be extruded. They can beexpanded.

They also have no splinters if the pencil breaks because they are basedon polymeric material.

DETAILED DESCRIPTION OF THE DISCLOSURE

According to a preferred embodiment, the lead casing for pencil of thedisclosure is made of a composition comprising (more specificallyconsisting essentially of, in particular consisting of), by weightrelative to the total weight of the lead casing for pencil:

a) from 70 to 90% of a mixture of PLA and bio-PE in a weight ratioPLA/bio-PE ranging from 60/40 to 90/10, andb) from 7 to 30% of vegetable fillers chosen in the group consisting ofwood fibers.

According to a preferred embodiment, the lead casing for pencil of thedisclosure is made of a composition comprising (more specificallyconsisting essentially of, in particular consisting of), by weightrelative to the total weight of the lead casing for pencil:

a) from 80 to 90% of a mixture of PLA and bio-PE in a weight ratioPLA/bio-PE ranging from 65/35 to 85/15, andb) from 10 to 20% of vegetable fillers chosen in the group consisting ofwood fibers.

The lead casing for pencil of the disclosure thus comprises a mixture ofPLA, for example commercially available from NaturePlast, and bio-PE,for example commercially available from Braskem, in a weight ratio ofPLA/bio-PE ranging from 60/40 to 90/10, in particular from 65/45 to80/20, more particularly from 70/30 to 80/20, and even more particularlyin a weight ratio of 70/30.

This mixture of biodegradable thermoplastic polymers serves as a matrixfor the lead casing for pencil of the disclosure and makes it possibleto manufacture the lead casing by extrusion and to provide goodmechanical properties such as resilience and impact resistance. It alsomakes it possible to bring the trimming to the lead casing for pencil ofthe disclosure. The content of the mixture of PLA and bio-PE in the leadcasing for pencil of the disclosure thus ranges from 50 to 95%, morespecifically from 60 to 92%, even more specifically from 70 to 90%, andeven more specifically from 80 to 90%, by weight relative to the totalweight of the lead casing for pencil.

In a preferred embodiment, the bio-PE of the disclosure is partially orcompletely bio-based polyethylene. The term “bio-based” as used in thedescription indicates the inclusion of some component that derives fromat least one material derived from renewable biological resources. Theminimum bio-based content of the bio-PE may be of at least 50% byweight, more specifically at least 60% by weight, even more specificallyat least 70% by weight, and even more specifically at least 80% byweight.

Bio-PE, also known as renewable polyethylene, is made out of ethanol,which becomes ethylene after a dehydration process. It can be made fromvarious feedstocks including sugar cane, sugar beet and wheat grain.

The polyethylene is more specifically a low-density polyethylene, alinear low-density polyethylene, a high-density polyethylene, anultra-high-molecular-weight polyethylene, a cross-linked polyethylene, ahigh density crosslinked polyethylene, a medium density polyethylene, avery low density polyethylene, as well as their copolymers and mixturesthereof. The polyethylene is more specifically a linear low densitypolyethylene, for example the green linear low density polyethylenecommercialized by Braskem under the reference SLH218.

The bio-PE of the disclosure more specifically presents a densityranging from 0.9 to 1.0.

The lead casing for pencil of the disclosure further comprises vegetablefillers chosen in the group consisting of wood fibers. The vegetablefillers make it possible to improve the mechanical properties of thelead casing for pencil such as the flexural modulus (3 points). Thevegetable fillers are chosen in the group consisting of wood fibers,more specifically in the form of powder, in particular commerciallyavailable from JRS Rettenmaier or CFF GmbH & Co. KG or Jelu-Werk orRossow.

More specifically, the vegetable fillers of the disclosure are combinedwith additional fillers such as for example shellfish shells, morespecifically milled shellfish shells. The shellfish shells are morespecifically oyster shells, and even more specifically milled (orcrushed) oyster shells. The additional filler can be more specificallymilled (or crushed) oyster shells, for example commercially availablefrom NaturePlast. The fillers can therefore consist of a mixture of woodfibers and shellfish shells, in particular a mixture of wood fibers andoyster shells such as milled (or crushed) oyster shells.

More specifically shellfish shells, even more specifically milledshellfish shells, and even more specifically milled (or crushed) oystershells, have a volume-average diameter (d50) ranging more specificallyfrom 10 to 160 μm, in particular from 20 to 100 μm, and moreparticularly from 30 to 80 μm. The volume-average diameter (d50) can forexample be measured by laser particle sizing with a Mastersizer 3000type apparatus commercially available from Malvern.

The total content of fillers (vegetable fillers+additional fillers) inthe lead casing for pencil of the disclosure may range from 5 to 50%,more specifically from 7 to 40%, even more specifically from 8 to 30%,more specifically still from 9 and 20%, and in particular 10% by weight,with respect to the total weight of the lead casing for pencil.

The content of vegetable fillers in the lead casing for pencil of thedisclosure ranges from 5 to 40%, more specifically from 7 to 30%, evenmore specifically from 10 to 20%, and in particular 15%, by weightrelative to the total weight of the lead casing for pencil.

The lead casing for pencil of the disclosure may further comprise anadhesion promoter. If the adhesion promoter is present, its contentranges from 0.1 to 10%, more specifically from 1 to 5%, even morespecifically from 2 to 5%, and even more specifically from 1 to 3%, byweight relative to the total weight of the lead casing for pencil. Theadhesion promoter makes it possible to improve the adhesion between thethermoplastic polymer (mixture of PLA and bio-PE) and the vegetablefillers.

Thus, in a particular embodiment, the lead casing for pencil of thedisclosure comprises vegetable fillers which consist of wood fibers,alone or possibly mixed with shellfish shells, more specifically milledshellfish shells, shellfish shells such as oyster shells, even morespecifically milled (or crushed) oyster shells, the lead casing forpencil also comprising an adhesion promoter as defined according to thedisclosure.

In a preferred embodiment, the adhesion promoter of the disclosure is apolylactic acid grafted with maleic anhydride (PLA-MA), for examplecommercialized by NaturePlast or NatureWorks.

The lead casing for pencil of the disclosure may comprise otheradditives, such as, for example, dyes and/or pigments, in particular inthe form of a masterbatch, for example based on PLA, blowing agents,agents for use, lubricants, slip agents such as stearates (calciumstearate for example) and/or stearamide, performance modifiers of PLA(melt enhancer which improve the strength/consistency of the extrusionmelt), in particular acrylics, and a mixture of these additives.

The content of additive in the lead casing for pencil of the disclosurewhen present ranges from 0.1 to 10%, and more specifically from 3 to 8%by weight, by weight relative to the total weight of the lead casing forpencil.

In particular, the lead casing for pencil of the disclosure may comprisea blowing agent, for example consisting of expandable and imperviousparticles, the wall of which is made of an extensible polymer material.Under the effect of temperature, a chemical or physical reaction occurswithin the particles, causing an increase in the internal volume of theparticles and their expansion. Thus, the blowing agent may be chosenfrom microspheres having a shell and enclosing a gas or a gas mixture.An increase in temperature causes an increase in the internal pressureof the microspheres that swell to a size that can be multiplied by fiveor more. Depending on the desired result of flexibility, weight, and anyother property of the material in which the blowing agent isincorporated, the expansion is completed or not.

More specifically, the blowing agent is introduced into the compositionof the lead casing in a content ranging from 0.1 and 1%, and even morespecifically from 0.5 and 1%, by weight relative to the total weight ofthe lead casing for pencil. The blowing agent is more specificallychosen in the group consisting of citric acid, sodium bicarbonate, ormixture thereof.

The lead casing for pencil of the disclosure may also comprise dyesand/or pigments (such as red iron oxide), in particular in the form of amasterbatch, more particularly based on PLA. The content of dyes and/orpigments more specifically ranges from 0.1 to 10% by weight, inparticular if the dye and/or the pigment is not in the form of amasterbatch, even more specifically from 0.1 to 5% by weight, and evenmore specifically from 0.5 and 3% by weight, relative to the totalweight of the lead casing for pencil of the disclosure. In a preferredembodiment, the dyes and/or pigments are capable of providing a colorclose to the wood to the lead casing for pencil of the disclosure.

The lead casing for pencil of the disclosure may be made of acomposition wherein the sum of weight % of component a) (mixture of PLAand bio-PE), components b) (vegetable fillers) and optional othercomponent(s) such as additional fillers, adhesion promoters, dyes,pigments, blowing agents, agents for use, lubricants, slip agents,performance modifiers, etc., represents 100%.

The lead casing for pencil of the disclosure is more specificallyextrudable. It is also more specifically shaped and can have inparticular the density and the sharpness approximating those of wood. Inparticular, the pencil can be cut by a traditional pencil sharpener.Therefore, it is not the lead casing for pencil of a mechanical pencil.

The present disclosure further relates to a pencil for writing, drawing,marking, plotting, and/or coloring, comprising a lead casing for pencilaccording to the disclosure. The pencil of the disclosure is not amechanical pencil. In the pencil of the disclosure, the lead casing morespecifically surrounds, in particular concentrically, the lead or aprotective intermediate layer disposed between the lead and the leadcasing of the disclosure. In a particular embodiment of the disclosure,the pencil of the disclosure comprises an additional layer ofdecoration, more specifically varnish, surrounding, in particularconcentrically, the lead casing of the disclosure. More specifically,the decorative layer is made of a material compatible with that of thelead casing of the disclosure.

According to a preferred embodiment, the lead of the lead casing of thedisclosure is a polymer-based lead, and not a calcined lead.

In a particular embodiment of the disclosure, the pencil of thedisclosure is obtained by extrusion, in particular by coextrusion of thelead/optional protective layer/lead casing according to thedisclosure/optional decorative layer. In a preferred embodiment, thecoextrusion makes it possible to prepare in a single step a continuousring consisting of the four aforementioned layers of the pencil, thesebeing assembled in the chosen order lead/optional protective layer/leadcasing according to the disclosure/optional decorative layer. For this,four single-screw extruders each delivering the material constituting alayer are connected in a coextrusion head tooling associating in theright order the layers between them.

Multiple extrusion techniques are well known to the person skilled inthe art. By way of example, such methods for continuously manufacturingpencils are described in document U.S. Pat. No. 6,572,295.

According to a preferred embodiment, the pencil of the disclosure is agraphite pencil and/or a colored pencil. The formulation of the lead mayvary depending on whether the pencil is a graphite pencil or a coloredpencil. An example of formulation of a graphite lead is described in theapplication WO2016/097553. The formulation of a colored lead may existin two forms: polyolefin-based erasable formulation as described in theapplication WO2016/097555 or styrenic-based standard formulation asdescribed in the application WO2017/220914.

In a particular embodiment of the disclosure, the lead has a diameter ofbetween 2 and 3.6 mm. In a graphite pencil, the diameter of the lead maymore specifically vary from 2 to 2.5 mm. In a colored pencil, thediameter of the lead may more specifically vary from 3 to 3.5 mm.

In the case of a graphite pencil, carbon black may be added to the lead,and thus considered as a pigment. In this case, graphite may vary from40 to 60% by weight and carbon black from 0 to 10% by weight, relativeto the total weight of the lead.

The pencil of the disclosure more specifically has a hexagonal, round ortriangular section, even more specifically round or hexagonal.

More specifically, the pencil of the disclosure comprises means forerasing, such as an eraser, at the uncut end of the pencil.

In addition to the above provisions, the disclosure also comprises otherprovisions which will emerge from the remainder of the description whichfollows.

Examples:

Two compositions A and B of lead casing were prepared.

Composition A (invention) was a mixture of PLA/bio-PE (NaturePlast PLE005-1 and Braskem SLH218) in a weight ratio of 80/20, added with 15% byweight of wood fibers (LIGNOCEL® JRS).

Composition B (comparative) was a mixture of polylacticacid/polybutylene succinate PLA/PBS (NaturePlast PLE 005-1 and PBE 003)in a weight ratio of 80/20, added with 15% by weight of wood fibers(LIGNOCEL® JRS).

Pencils with hexagonal section were manufactured by coextrusion with acolor lead made of acrylonitrile-butadiene-styrene (ABS) (composition in% by weight relative to the total weight of the lead: 40% ABS copolymer,12.5% kaolin, 27.5% calcium stearate, 20% additive), a sheath, a leadcasing of composition A (invention) is or of composition B(comparative), and a varnish. The thickness of the lead casing is 4.5mm.

The performance of the pencils made of the lead casings of compositionsA and B were tested according to the following tests:

The sharpen strength resistance test was measured in order to assess theforce needed to cut a pencil. The characteristics of the test were asfollows:

Equipment: computer, force sensor (AMETEK Sensors) and cutting device

Descent speed of the pencil: 70 mm·min⁻¹

Operating mode:

1. Locate the pencils and indicate the weight of each pencil.

2. Check that all three devices are on.

3. On the moving part of the pencil sharpener, use the appropriatesupport depending on the pencil to be tested.

4. Fix the pencil in the chuck, not cut side.

5. Lower the pencil holder by acting on the clip to engage the sharpside of the pencil in the hole of the device.

6. Turn on the sharpener.

7. Record the results after stopping the pencil sharpener.

The results were expressed in N·mm.

The lead resistance at 45° of the pencils made of the lead casings ofcompositions A and B was tested with a Dynamometer Chatillon instrumenttype TCM 201-M, according to the following operating mode:

1. Position the pencil in a support with a 45° inclination, descend thepencil at a descent speed of 50 mm·min⁻¹, and come into contact with ametal plate until the lead breaks.

2. Read the value of the result displayed on the dynamometer.

The result was the measure of the force required to break the mine,expressed in daN.

The results of the pencils made of the lead casings of compositions Aand B are summarized in the following Table 1:

TABLE 1 Composition A Composition B (invention) (comparative) Sharpenstrength resistance 89.58 159.52 (N · mm) Lead resistance at 45° (daN)2.06 1.46

The results presented in Table 1 show lower sharpen strength resistancefor composition A (invention) than for the comparative composition B. Alower value of sharpen strength resistance means that a lower force isrequired to sharpen the pencil of the disclosure, thereby improving theease of sharpening. In addition, there was no problem with the lead madeof the lead casing of composition A during the sharpening of the pencil:the lead did not break and did not take off the pencil.

The results presented in Table 1 also show better lead resistance at 45°for the pencil according to the disclosure made of the lead casing ofcomposition A with respect to the comparative pencil made of the leadcasing of composition B.

1-10. (canceled)
 11. A lead casing for a pencil, comprising acomposition including, by weight relative to a total weight of the leadcasing for the pencil: a) from 50 to 95% of a mixture of polylactic acidand bio-polyethylene in a weight ratio polylactic acid/bio-polyethyleneranging from 60/40 to 90/10, and b) from 5 to 40% of vegetable fillersselected from the group consisting of wood fibers.
 12. A lead casing forthe pencil according to claim 11, comprising, by weight relative to atotal weight of the lead casing for the pencil: a) from 60 to 95% of amixture of polylactic acid and bio-polyethylene in a weight ratiopolylactic acid/bio-polyethylene ranging from 60/40 to 90/10, and b)from 7 to 30% of vegetable fillers selected from the group consisting ofwood fibers.
 13. The lead casing for the pencil according to claim 11,comprising, by weight relative to the total weight of the lead casingfor the pencil: a) from 80 to 90% of a mixture of polylactic acid andbio-polyethylene in a weight ratio polylactic acid/bio-polyethyleneranging from 65/35 to 85/15, and b) from 10 to 20% of vegetable fillersselected from the group consisting of wood fibers.
 14. A lead casing forthe pencil according to claim 11, wherein the weight ratio polylacticacid/polybutylene adipate terephthalate is ranging from 65/45 to 80/20.15. The lead casing for the pencil according to claim 11, wherein thecomposition comprises an additional filler different from the vegetablefillers.
 16. The lead casing for the pencil according to claim 15,wherein the additional filler is selected from the group consisting ofshellfish shells.
 17. The lead casing for the pencil according to claim15, wherein the additional filler is milled oyster shells.
 18. The leadcasing for the pencil according to claim 11, wherein the total contentof filler ranges from 5 to 50%, by weight, with respect to total weightof the lead casing.
 19. The lead casing for the pencil according toclaim 11, wherein the total content of filler ranges from 7 to 40%, byweight, with respect to total weight of the lead casing.
 20. The leadcasing for the pencil according to claim 11, wherein the total contentof filler ranges from 8 to 30%, by weight, with respect to total weightof the lead casing.
 21. The lead casing for the pencil according toclaim 11, wherein the total content of filler ranges from 9 to 20%, byweight with respect to total weight of the lead casing.
 22. The leadcasing for the pencil according to claim 11, wherein the content ofmineral filler ranges from 5 to 40% by weight, relative to the totalweight of the lead casing.
 23. The lead casing for the pencil accordingto claim 11, further comprising at least one additive selected from thegroup consisting of dyes, pigments, blowing agent, agents for use,lubricants, slip agents, performance modifiers of polylactic acid, andtheir mixtures.
 24. The lead casing for the pencil according to claim14, wherein the additive represents from 0.1 to 10% by weight, relativeto the total weight of the lead casing for the pencil.
 25. The leadcasing for the pencil according to claim 11, further comprising anadhesion promoter.
 26. The lead casing for the pencil according to claim25, wherein the adhesion promoter is a polylactic acid grafted withmaleic anhydride (PLA-MA).
 27. A pencil comprising a lead casing for thepencil according to claim 11 surrounding a lead.
 28. The pencilaccording to claim 27, wherein the lead includes at least graphiteand/or pigments.
 29. The pencil according to claim 27, being a graphitepencil and/or a colored pencil.
 30. A method for manufacturing a pencilaccording to claim 27, wherein the constituents of the lead casing forthe pencil are coextruded around the constituents of the lead.